Hi there. I am a compulsive gambler, and I go to GA (in fact, I am the chair at the local meeting). My last bet was 15/09/2012.
Firstly, your partner has to want to give up. It's not enough to just tell you that he wants to do, he has to want to himself. He'll lie about it, but then, he'll lie about anything.
However, GA will help him, and there are a lot of people in GA who have many years of abstinence, as well as lots of people who haven't.
He should try to attend as many meetings as possible in the first 3 months, as this is the most difficult period. No-one will judge him - everyone there has the same problem. After that, he should try to develop a routine where he attends meetings regularly, with no excuse. There is no substitute for the meetings. The majority of people who relapse in GA tend to be tardy in attending meetings.
Even if he goes only once, he should get all the literature that he can. I think the orange book is incredible and it has helped me tremendously. The 12 step program and living one day at a time were and are my lifesavers.
Don't worry about the 12 steps however - that can come later (but is very important). If he can get a sponsor all the better but that's not always that easy.
There are practical things that can and should be done. He should hand over control over all of his money and live off a budget that you control. That includes passwords for banking sites - I'm assuming he trusts you. He should self-exclude from bookies if that's his poison, and install blocking software on all PCs/smartphones if that's how he gets his fix (actually, you should do the installation so he doesn't know the password). Try k9webprotection.com, which is free.
The urge to gamble actually doesn't last very long (but can be very strong). Compulsive gamblers tend to respond to it immediately, but stopping and focussing on something else for 30 seconds will nearly always get you through it.
It is a hideous disease (it IS a disease, no matter what anyone else will tell you) but it can be controlled. I liken it to diabetes (sorry to any diabetes sufferers out there) - follow the advice of other sufferers in control.
He will have to face the financial consequences of his gambling too, but that is secondary to getting the compulsion under control.
If you have ANY questions about compulsive gambling please ask - I'm more than happy to answer them.
btw. there is an online forum at gamblersanonymous.org.uk, but it's very quiet there normally. There's normally someone though, who can offer advice.